CA1081520A - Process for the preparation of matted photographic layers containing gelatine - Google Patents

Abstract

PROCESS FOR THE PREPARATION OF MATTED PHOTOGRAPHIC
LAYERS CONTAINING GELATINE

Abstract of Disclosure In a process for the preparation of matted photographic layers gelatine particles which are dispersed in a water-in-oil emulsion are hardened, separated from the emulsion, redispersed in water, added to the layer which is required to be matted, and the casting composition is applied to a substrate and dried.

Description

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This invention relates to a process for the preparation of matted photographic layers using modified gelatine.
It is known to use dispersions of inorganic or organic pigments or synthetic resins for rendering photographic layers matt. All these matting agents have the disadvantage of having a distinctly di~ferent refractive index from that of gelatine which is used as binder for the photographic layers and generally constitutes the major component of such layers. The matting agents cause substantial clouding of the photographic layers and thereby reduce the sharpness of the image. In addition, they have no capacity to swell, they act as foreign bodies in the layers and they have a damaging effect on the mechanical properties of the layers and interfere with the diffusion processes in photographic development.
It is also known to produce matted photographic layers by milling gelatine powder in a volatile organic solvent such as ethyl alcohol which contains formaldehyde, displacing the solvent with another, non~polar organic solvent such as benzene, evaporating off the non-polar solvent and using the hardened gelatine powder for matting the photographic layers~ if necessary first redispersing the powder in water as described in U.S. Patent No. 2,043,906. One disadvantage of this process, however, is that even the most vigorou~ milling can only produce relatively coarse particles which moreover vary considerably in size. The matt ef~eot produced in photographic layers containing these substances is too coarse ~or most purpose~.
-` It is therefore an objeot of this invention to develop a process by which a more uniform and finer matt ef~eot can be obtained and which enables the degree of matting to be adjusted ~815Z~

to different ~equirements with quite simple means and which avoids optical defects due to the matting agent~
The invention relates to a process for the p~eparation of matted photographic layers containing gelatine as a binding agent, using a casting composition which contains haTdened gelatine paTticles as a matting agent, characterized in that gelatine particles dispersed in a water~in-oil emulsion containing a non-polar solvent as OTganiC phase in the presence of an emulsifier having an HLB~value from 3 to 8 ~"hydrophilic-lipophilic balance";
see house magazine of Atlas Chemical Industries, 1963 "Das Atlas HLB-System") and of a hardeneT are hardened, the hardened gelatine particles are sepaTated from the emulsion and redispersed in water and the aqueous dispersion so formed is added to the casting composition of the layer which is to be matted~
the quantity added being calcu?ated so that its proportion of the dry weight of the binder content of the layer is not greater than 50% by weight1 and in that the casting composition is applied to a substrate and dTied.
The aqueous dispersions of hardened gelatine particles used as matting agents according to the invention are obtained from aqueous gelatine solutions which are first emulsified in a non-polar organic solvent with the aid of emulsifiers to form a water-in-oil enwlsion in known manner. A
hsrdeneT which is soluble in the non-polar solvent is then added to the gelatine emulsion. The hardened gelatine pa~ticles are separated from the emulsion, the organic solvent is ~emoved and the gelatine particles are finally redispersed in water. A description of the W/0 emulsification pTocess and of suitable emulsifiers and apparatus for this pTOCeSS is given by J. Stauff in Kolloidchemie, Springer-Verlag 1960, pages 509-519.
Examples of suitable non-polar organic solvents for the preparation , , . q, !

~6~8~0 of the oil-in-water em~lsions include higher boiling petroleum hydrocarbons such as cleaning petrol or ligroin, higher boiling paraffins such as C6 to C16 hydrocarbons, toluene, xylenes, monoethyl-, diethyl, triethyl- or propylbenzene, mesitylene, tetramethyl_and pentamethylbenzene, further biphenyl, di-phenylmethanefperchloroethylene and carbon tetrachloride.
Any of the known water-in-oil emulsifiers may be used for emulsi~ying the aqueous phase in the oil phase, pre~erably those with low HLB values (hydrophilic-lipophilic balance;

lo see house magazine of Atlas Chemical Industries, 1963 "Das Atlas HLB-System") and preferably HLB values of from 3 to 8 An emulsifier which has proved to be particularly suitable ~or the system ~f cleaning petrol/aqueous gelatine solution consists of a mixture of glycerol monodioleate and polyethylene glycerol monooleate used in proportions by weight of 6:4 while sorbitan dioleate is particularly suitable for $he system perchloroethylene/
gelatine solution. Other examples of suitable emulsifiers include the monooleate, stearate, laurate and palmitate of sorbitan; poly-oxyethylene-sorbitan fatty acid esters, i.e. reaction products of 1 mol of the given sorbitan fatty acid eeter and 4 to 40 mol of ~` ethylene oxide, and polyoxyethylene sorbitol esters of ~atty acids and resinic acids and mixtures thereof. Further suitable emulsifiers may be found in "Ullmans Encyklopadie der techni-schen Chemie, 4. Au1. Bd. 10, pages 462 and 463, tables 3, 4 and 5. l'ne concentration of the emulsifier generally depend on the used system solvent/emulsifier. In some cases concentra-tionsof only 1% by weight of emulsifier are suitable, in : particular if immediately after the emulsification the mix-ture is cooled down to room temperature. A survey of emulsifiers l~lS~

suitable for the process acc~rding to the invention and their HLB values may be found in the report by F.H~lscher "Dispersionen synthetischer Hochpolymerer" ~rom the series ~'Chemie, Physik und Technologie der Kunststo~fe in Einzeldarstellungen1' (Springer-Verlag l969~, pages 58 and 59, and Schlick "Nonionic Surfactants" Vol.l, pages 609 - 611.
Any of the known hardenable gela~i~s may be used in the process of the invention, i.e. as well acid treated as alkaline treated gelatineSor mixtures thereof, further the numerous hardenable gelatinederivatives or modified gelatines such as described for example in the US Patent Specifications

2 920 o68, 3 o61 436, 3 782 955, 2 794 787, 2 713 575 or 2 688 610.
Moreover it is possible to replace gelatinein the process of the inven~ion by other highmolecular substances which are hardenable. As examples may be mentioned synthetic polypetides, watersoluble cellulose derivatives, vinyl- or acryl-polymers or -copolymers containing carboxylic acid-, sulfonic acid- or acid amide groups. The polymers may be hardened by means of the known hardening agents reacting with carboxylic and amino groups.
The hardeners used should be at least partly soluble in the organic solvent. Although hardeners which are insoluble in the organic solvent could conceivably also be emulsified in the water-in-oil emulsion~ it is then necessary to ensure that the hardening reaction does not set in until the emulsion has been completely prepared. This can be ac~ieved, for example, by using a slow acting hardener. Formalin, glyo~al and penta-dialdehyde are examples of suitable hardeners although other~
could also be chosen from the long list of compounds known as 15Z~

hardeners ~or p~oto~raphi~ layers provided that they harden su~Eiciently slowly not to inter~`e~ with the preparation o~ the water~ oil emulsion.
However, it is also possible to use so-called fast acting hardeners such as carbamoyl pyridinium or carbamoyloxy pyridinium salts as described in the U.K. Patent Specification 1 383 630, the German Offenlegungsschrift 2 439 551 and the Belgian Patent Specification 825 726, carbodimimides as des-cribed in the US Patent Specifications 2 938 892 or

3 o98 693, dihydroquinoline compounds as des-cribed in`the Belgian Patent Specification and isoxazolium salts and bis-isoxazoles as described in the US Patent Specifications 3 316 o95, 3 321 313, 3 543 292 and 3 681 372 or the U.K. Patent Specification 1 o30 882. The application of fast acting hardeners requires a certain modification of the emulsifying process which will be explained in the follow-ing.
It may still be mentioned that a slow reacting hardener such as triacrylformal or chromium acetate can be added to the aqueous gelatin~solution already before the preparation of the emulsion. After emulsification the reaction of the hardener can be accelerated by changing the pH-value of the mixture, by increase of the temperature or by distilling off the bulk of the water from the W/O system, preferably under vacuum at room te~perature. If fast reacting haxdeners are used, the operating time must be adapted to the reaction time of the hardener, i.e. the period of emulsification must be shorter than the reaction time of the hardener. On the other hand ~f3lSZ~

it is possible to carry out the emulsification at p~ ranges wherein the reactivity of the hardeneriS low and then to adjust ~he pH value, for example by adding volatile or easily soluble bases or acids such as ammonia or acetic acid, to the optimum S pH at which the hardener develops its optimum reactivity.
The preferred and simplest procedure of course com-prises as a first technological step the emulsification of the gelatin solution up to the desired fineness of the gelatine particles and as the second chemical step the hardening of lo the obtained gelatineparticles. In the second step for example the hardener can be added in solid form i~ it is soluble in the organic solvent to some extend and can diffuse into the aqueous medium. However, the most favourable method consists of preparing the W/0-gelati~ emulsion and adding an aqueous solution of the hardener emulsified in the tensid containing organic solvent which already is part of the gelatineemul~ion. In this way an especially uni~orm hardening of the gelati~ particles can be obtained.
Any of the known mixing apparatus which have a high shear gradient may be used as dispersion apparatus for preparing the water-in-oil emulsions and for subsequently redispersing the hardened gelatine particles.
The procedure described above can be used for emulsifying and hardening aqueous solu~ions containing from 6 to 30% by weight of gelatine. More highly concen-trated solutions are too viscous for this method and give rise to excessively coarse gelatine particles. Where it is necessary to start from more highly concentrated gelatine solutions, the gelatine may be hydrolysed or bro~en down by enzyme action, for example with the aid of pepsin, papaill or trypsin.
The matting process according to the invention may be applied to photographic layers which contain gelatine as binder, in other words it is applieable both to light-sensitive emulsion layers and to light insensitive photo-graphic auxiliary layers such as protective layers, interlayerg~ filter layers or backing layers. The process is mainly intended for matting the outermost layers o-f photographic materials, for example the exposed silver halide emulsion layers, protective layers and/or backing layers. On the other hand, it may also be advantageous to matt internally situated layers such as interlayers or filter layers in order to prevent damage such as tears or patches due to contact or sticking during the individual stages o~ the process of manufacturing multilayer photographic materials.
In the process according to the invention~ the dispersions of the matting agents are added to the casting 2 compositions of the photographic gelatine layers so that, in the case of protective layers, from 5 to 50~ by weight of the gelatine in the casting composition9 generally lO to 30~ by weight~ is replaced by modified gelatine. ~hese figures are based on the dry weight of gelatine.

The size of the hardened gelatine particles obtained and hence the fineness of the matt effect can easily be influenced by controlling the condition~ under which the emulsifyine process is carried out. Increa~ing the quantity 315Z~

of the emulsifier used results in smaller particles and therefore finer matting. Smaller particles are also obtained by more vigorous mixing, a longer emulsification time and lower viscosity of the gelatine solution. If gelatine particles with a very low capacity to swell are required for certain purposes, the water-in-oil e~ulsion may first be further dehydrated and then hardened. Dehydration can be effected by the addition of dehydrating agents such as calcium chloride and sodium sulphate or by azeotropic distillation of the emulsion and return of the organic solvent. Gelatine lo concentrations of up to 50~ can be obtained in this way.

The volumetric swelling is determined by the following method:
100 ml of aqueous gelatine dispersion are centrifuged until there is no further change in the volume of sediment of gelatine particles. The swelling factor Q can be calculated from the absolute gelatine content in g, the specific gravity of gelatine (1.3) and the volume of sediment V according to the ~uation Q = V . 1.~

g The process according to the invention makes it possible for exceptionally fine grained matted photographic gelatine layers to be obtained~ The advantage of a ~ine grained matt effect is particularly important when the process according to the invention is used for matting extremely thin layers which form constituents of mult~layered photo-graphic materials, e.g. colour photographic material~.

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Moreover, using modified gelatine particles as matting agent has the effect that the refractive indices of -the binder and matting agent are substantially identical, thus avoiding the undesirable optical effects which are particularly S troublesome in photographic materials. Another advantage of using matting agents made of modified gelatine is that their swellin~ properties are very similar to those of the binder used for the layer so that the matting agents in no way interferewith the penetration of the processing baths lo into the layers.
The following Examples serve to explain the invention in more detail.

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Example 1 (a) Preparation o~ the matting dispersion 0.18 kg of glycerol monodioleate (HLB ~alue 3.3) and 0.12 kg of polyoxyethylene glycerol monooleate (HLB
value 15) were dissolved in 20 litres of cleaning petrol.
30 Litres of a 20~ gelatine solution at pH g ~ere then emulsified in the aforesaid solutioIl at 40C with the aid of a high speed stirrer. An emulsion of 1.33 litres of 30~ formalin solution in 1.33 litres o-f the above surface-active solution in petroleum hydrocarbons w~ added for hardening. After a hardening time of 2 to 3 days at room temperature, the emulsion was poured into 150 litres of methanol and 0.135 litres of glacial acetic acid to break up the emulsion. When the precipitate ~ad settled, the petroleum hydrocarbon which separates as a supernatent layer was siphoned off and the precipitate w~ ~iltered and washed free from sur~actant with the methanol. The precipitate ~asstirred into water while still moist, using a h~gh speed stirrer. A gelatine dispersion containing 5~ of gelatine wasthereby obtained.
The size o~ the gelatine particlesw~ in the region of 5 to 20 ~ and the volume of the particles a~ter swellingwas 5 times the volume of the particles before swelling (swelling factor = 5).
(b~ Preparation of a matted photographic layer Four photographic silver bromide ~elatina emulsi~ns ready for casting were used, each containing 10~ by weight oi gelatine. In three o~ the emul~ions, ~, 10~ and 20~ by weight, respectively, of the gelatine was replaced by corresponding quantities by weight of the dispersion o~
matting agent described above. The ~our examplesWere cast ~8~S2~

to form layers 10 ~ in thickness on a cellulose triaeetate substrate covered with a bonding lay~r~ and they were then dri~d.
The roughness of the sur~ace of the la~erW~ then determined by measuring the peak to valley height by mea~s of a "Hommel-Tester Type T" surface measuring instrument manufactured by Hommelwerke GmbH, Mannheim-Kafertal. The results are summarised in the following Table.

Proportion of matting Peak to Valley height in dispersion in the binder the surface of the layer in content of the emulsion Pure gelatine 0.2 - 0.4 5~ by weight 1.0 - 2.0 10~ by weight 1.5 - 2.5 20~ by weight 2.0 - 3.0 50~ by weight 2.5 - 3.5 Emulsion layers which contain more than 10~ by weight oi the matting dispersion as binder are excellent for retouching purposes.
Example 2 (a) Matting dispersion 0.72 kg oE glycerol ~onodioleate (HLB value 3.3) and 0.48 kg o~ polyoxyethylene glycerol monooleate (H~B
value 15)~ere dissolved in 20 1 o:E cleaning petrol. The procedure was otherwise the same as that described in Example 1. The size of the dispersed gelatine particles wa9 in this case in the region o-~ -Erom ~ to 10 ~ while the volumetric swelling was unchanged.
(b) Preparation oE the photographic silver halide emulsion 3o layerw~ carried out as in Example 1 but only one emulsion ~8~5Z~) layer w~ cast. It contains 10% by weight of matting a~ent based on ~he total weight of binder. The matt iinish on the surface of the layer was in this case ~iner and had a peak to valley height of 1 to 2 ~.
Example ~
(a) Preparation of the matting dispersion was carried out as in Example 2 but using a 10% gelatine solution in~tead of the 20% gelatine golution. The procedure w~ otherwise the same as in Example 1. The size of the particles obtained ~Jasfrm 3 to 5 ~ and the swelling volume w~ about double (swelling factor 10) that obtained in Examples 1 and 2.
The procedure described in Example 1 was varied in that the filtered and washed product w~ stirred up in water to form a 3% dispersion of matting agent.
(b) A silver halide emulsion containing 10% by weight of gelatine and no matting agentw~ cast on a prepared cellulose triacetate substrate as described in Example 1 and dried.
A protective gelatine layer containing 250/o by weight of the matting di~persion described abovewas applied to the silver halide emulsion layer in a thickness o~ 1 ~u.
~he surface of the dried protective layer had a peak to valley height of 1 to 1.5 ~ and was very suitable for retouching.
Example 4 (a) The method of preparation of the matting dispersion described in Example 1 was modified by increasing the weight of glycerol monodioleate from 0.18 to 0. 72 kg and the quantity of polyoxyethylene glycerol monooleate from 0.12 to 0.48 kg and using 2.66 1 instead of 1.33 1 of formalin solution ( 30%) for hardening.
The dispersion prepared in this way contain~d particles measuring from 5 to 10 ~u as in Example 2 but, ~C~8~52~) since double the quantity of hardener was uged, -the pRrticles had a greater dimension stabi1ity and a more powerful matting effect.
The matting dispersion was u~ed for preparine protective layers as described in E~ample 2b. Two ~amples ~J~re prepared~ one eontaining lO~ by weight ol` the matting dispersi~n in a protective gelatine layer (sample l) and the other 20~ by weight (sample 2). The following results t~ereobtained Sample l Peak to valley height l.5 - 2.5 ~
Sample 2 Peak -to valley height 2,0 - 3.0 p.
Example 5 (a) The preparation of the matting dispersion w~ initially carried out by the procedure described in Example l, ueine 0.72 kg of glycerol monodioleate and 0.48 kg of polyoxyethylene glycerol monooleate in 20 l of cleaning petrol. In this case, however, the resulting emulsion was distilled in a thin layer evaporator at 40C under vacuum and dehyrated. The solvent used for distillation was returned to the omulsion.
Distillationwas continued until the emul~ified gelatine solution had a concentration of about 50% by weight. It wasthen hardened and processed as described in Example l.
The particles obtainedwere smaller than thoee in Example 2 and range from 3 to 7 Ju. The volumetric swelling waseven further reduced and amounts to 2,5, (b) A photographic material having a protective gelatine layer was prepared as described in E~ample 3. It contained the proportion of matting agent given in the ~aid e~ample.
The matting effect obtained in thls way was substantially more fine grained than that obtained in Example 2 but at the same time the surface had a greater pea~ to valley height, amounting to 1,5 to 2 ~.

? A-G 1280 ~ 14 -~, , , : .

5~0 This is presumably because the particles harderled in a more highly concentrated form are less capakle of deformation. They retain their ~pherical shape even after drying whereas the particles obtained by the methods used in the previous Examples dry to a lentil shape.
Example 6 (a) A matting dispersion described in US Patent No. 2,043,906 wasPrePared as follows:
10% by weight of gelatine powder were added to a 1% formaldehyde solution in absolute alcohol and dispersed in a ball mill for 12 hours. The alcohol was then replaced by benzene and the benzene was distilled off. A gelatine powder forming a 5% by weight dispersion in waterwas obtained.
The size of the particles fluctuate widely between 2 and 15 ~.
(b) The 5% aqueous gelatine dispersionwas used for preparing a matted silver bromide gelatine emulsion layer as indicated in Example 1 (b).
A peak to valley height of 8 to 12 ~ was obtained.
Compared with the corresponding layer obtained in ~xample 1, the matted layer had a clearly more visible grain in the photographic image.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 A process for the preparation of matted photographic layers containing gelatine, using a casting composition which contains hardened gelatine particles as a matting agent, characterized in that gelatine particles dispersed in a water-in-oil emulsion containing a non-polar solvent as organic phase in the presence of an emulsifier having an HLB-value from 3 to 8 and of a hardener are hardened, the hardened gelatine particles are separated from the emulsion and redispersed in water and the aqueous dis-persion so formed is added to the casting composition of the layer which is to be matted, the quantity added being calculated so that its proportion of the dry weight of the binder content of the layer is not greater than 50%
by weight, and in that the casting composition is applied to a substrate and dried.

2, Process according to claim 1, characterized in that an aqueous gelatine solution is emulsified in the non-polar solvent in the presence of emulsifiers and a second emulsion of an aqueous solution of the hardener in the non-polar solvent containing an emulsifier is added to the first emulsion, the hardened gelatine particles are separated from the mixture, redispersed in water and the dispersion is added to the casting composition of the layer which is to be matted.

3, Process according to claims 1 and 2, characterized in that the casting composition applied is one in which the binder contains from 5 to 50% by weight of hardened gelatine particles, based on the binder content of the dry layer.

4, Process according to claim 1 and 2, characterized in that the organic solvent used is cleaning petrol and the emulsifier used is a mixture of glycerol monodioleate and polyethylene glycerol monooleate in proportions by weight of 6 : 4.

5. Process according to claims 1 and 2, characterized in that the hardener used is formaldehyde.